NA6 - Rear damper travel & bump stops

[Magpie]

Has anybody tracked their NA6 without rear bump stops or with a 'thin hard spacer'?

Interested to know as it would appear that the damper is not doing anything when the car is fully on the bump stops, plus the spring rate is 'un predictable' when bump stops are fully compressed.

This is going through T1 and looking at the RR damper.

At rest the RR ride height is 175mm, however the ride height settles at 150mm and the shock velocities 'settle' for most of the time in the corner. It is only at the start/end of the corner when the ride height is changing are the shock velocities 'active'.

This could imply that the rear is already on the fully compressed bump stops and the damper is essentially doing 'nothing'.



When dropping off the BC's for a health check had a very interesting discussion about damper travel and what information one really needs to know before starting on making changes to the suspension.

[93_Clubman]

This could imply that the rear is already on the fully compressed bump stops and the damper is essentially doing 'nothing'.

That's my understanding.

[Magpie]

That's my understanding.

I just realised that was a captain obvious statement

Have been given some advice that is food for thought, however it all depends on the outcome of the damper testing... Depending on the outcome it will be looked at if the dampers can continue into the next project.

"Cut the bump rubbers down by half to start with. I'd also be zeroing your shock positions at ride height for ease of reading later. It's a PITA as you have to do it whenever you finish a setup. Alternatively, start a math channel using the static position as an offset so it reads zero at ride height. It also helps visualising the attitude of the car a lot."

The current 'Fatcat' bump stops


Looks like it will be busy period in December/January just like last year!

[93_Clubman]

My reading of your post was that you were emphasizing that it was running on compressed bump stops, as opposed to emphasizing a redundant damper. Tbro was one of the earliest that did some work in relation to this on his track Clubbie, & posted about it, but post's about a decade old & seems to be MIA, or at least a quick search isn't locating it.

[Magpie]

My reading of your post was that you were emphasizing that it was running on compressed bump stops, as opposed to emphasizing a redundant damper. Tbro was one of the earliest that did some work in relation to this on his track Clubbie, & posted about it, but post's about a decade old & seems to be MIA, or at least a quick search isn't locating it.

When the forum was cleaned up a while ago and the index was removed to search old posts

Yes it, well at least to me is running on compressed bump stops hence there is an amount of damper travel that is now not being used because of the compressed bump stops.

When I set the damper length, it was done without the bump stops installed, hence the now fully compressed bump stop is not allowing the damper to compress to its limits.

[plohl]

I am running cut down bump wrx bump stops in the rear, there's evidence to say I am hitting them every now and then. They're about 10 to 12mm thick.

It was literally what I could get my hands on at the time.

What's your shock compressed length? About 240mm off the top of my head is all you could use before the standard top arm starts hitting the chassis.

How much travel do you on the shocks?

[Magpie]

I am running cut down bump wrx bump stops in the rear, there's evidence to say I am hitting them every now and then.

Thanks!

I'm not sure what the fully compressed length is, however I have 70mm of damper travel in the rear. When the dampers come back I will re-set everything back up (with cut down bump stops) and take notes...

The discussion on Sunday was also around that the amount of travel in the rear could be governed by the chassis as well as drive shafts etc.

[Magpie]

Almost lived in the shed from Fri afternoon to Sunday night. Friday evening and Saturday morning was spent rolling guards on the rear after a test fit of the rear dampers showed that the tyre would contact the guard.

Now can do coilover setup 3 ways

1. Set 'preload' on springs and adjust ride height by lower collar. Plus - very quick, very popular and for most works. Cons - changes damper lengths which could cause tyres to rub or not use all the available stoke and or not have sufficient droop/bump
2. Set damper length first, then adjust ride height from spring perch. Plus - nothing rubs. Cons - requires dampers to be pulled apart, re-fitted, then length of damper adjusted. Pull back out, reassemble and set ride heights from spring perch. The pulling out only needs to be done on one side, as the length duplicated for the other side. Can be a lengthy process, but does give a better result than the first.
3. Set the required bump travel first, then adjust ride height by adjusting the damper length. Plus - bump travel is known, bump stops can be modified so that each side engages the bumps stops after the same amount of bump, an excuse to purchase/fabricate hub stands. Cons - VERY long process, actually measuring the bump/stroke with springs installed, may have rubbing issues then the decision will need to be made to sacrifice some bump travel, changing spring rates requires the whole process to be done again.

After the test result came in for the BC Racing ER's, not only was I given recommended settings, but was informed that there was very little travel in the rear (any NA6 owner knows this) and at the absolute minimum need 100mm of wheel travel (70 bump and 30 rebound).

Number in bracket is wheel travel, ride height with driver. I started on the RR but after doing the LR had to revisit the RR. When you consider the installed bump stops were 38mm, this only left about 5mm (7mm) of travel before they engaged. When engaged the spring rate became variable
Rear Left (damper travel)
43.3 bump (60.1)
33.1 droop (45.9)
5mm bump stop
124 ride height pinch weld
329 fender

Rear Right
47.6 (66.1) bump
26.6 (36.9) rebound
5mm bump stop
125 pinch weld
327 fender

Previous/revised bump stop size.




As it ended up


In case interested the radius (at 32 psi) for 205/50/15 AD08R's is 275

[Magpie]

Made a full post on how the measurements were done here https://www.facebook.com/notes/team-racepak/diagnosing-a-suspension-issue-part-2/2227389620878290/

Too difficult to reproduce here, plus it is part of my obligations to Racepak